1. Field of the Invention
The invention relates to a cold pilger rolling mill with a roll stand that can be moved back and forth, which is connected via two thrust rods to the crankpins of two cranks, and the inertial forces of which can be at least partially balanced by counterweights in the form of centrifugal weights attached to the cranks eccentric to the rotational axis of the cranks and staggered by 180 degrees to the linkage point of the thrust rods.
2. Description of the Prior Art
In conventional cold pilger rolling mills, tile back and forth movement of the roll stand is produced by crank mechanisms of various types. During rolling, the large moving inertial masses of the rolling mill produce very great inertial forces, which necessitate countermeasures in order to reduce vibrations. In the simplest models, the countermeasures are limited to the attachment of counterweights to the crank of the crank mechanism. However, such measures achieve only a poor balance of mass and are not suitable for preventing the vibrations.
Most cold pilger rolling mills are equipped with a torque and mass compensation system which permits the complete compensation of mass forces of the first order as well as very good torque compensation. A known cold pilger rolling mill accomplishes this by means of a torque compensation system, connected to the crank mechanism, which stores the kinetic energy that is released during the deceleration of the roll stand to a dead center position in a counterweight that is attached to the crank mechanism staggered by 90 degrees and can be vertically moved up and down, and then re-uses this energy during the subsequent acceleration of the rolling mill. This vertical torque compensation system, incorporating the roll torque on the forestroke and the backstroke, frees the entire drive between the drive motor and the crankshaft from temporarily back-flowing kinetic energy. In other words, at a constant crank speed, the drive moment is also constant to a great extent, because the kinetic energy flows back and forth between the subgears without placing a load on the motor ("Machines and Equipment for the Production of Tubes using the Cold Pilger Process," in Mannesmann Demag Huttentechnik, pp. 18 and 19). Although this known design addresses the requirements for adequate mass and torque compensation, it has the disadvantage of requiring deep foundations which represent a considerable share of investment costs. Another disadvantage is that expensive split beatings must be used on the crank throws and as the middle crankshaft bearing.
For small-sized tubes, the use of planetary crank mechanisms, which also allow complete mass compensation and complete torque compensation, has been suggested. Non-split bearings can be used with these rolling mills and deep foundations are not required; however, this design cannot be carried over to cold pilger rolling mills for large-sized tubes.
Finally, DE 41 24 691 C1 suggests simplifying the crank mechanism of a cold pilger rolling mill by constructing this mechanism of three parallel and equidistant shafts, with the middle shaft being designed as the crankshaft and linked via its crankpin to the thrust rod connectable to the roll stand. A main weight is attached eccentric to the crank in staggered fashion, and located on the two other shafts are auxiliary weights, which together are to balance the inertial mass of the roll stand. This drive configuration does indeed allow complete mass force compensation of the first order with the use of non-split bearings; however, it also requires relatively deep foundations, because the entire mechanism, including the drive pins, balancing weights, bearings, gearwheels and housing, must be located underneath the fixed center of the roll in order to permit the rolled tube to emerge freely. When the minimum heights for these components are added to the total height of the mechanism, deep excavations in the foundation again become necessary, particularly in the case of cold pilger rolling mills for large-sized tubes. Furthermore, the known suggestion does not provide for any countermeasures against the non-uniformity of the crank angle speed.